How to Use Coupons on Steamby Seth Amery ; Updated September 22, 2017
Unlike other online stores, Steam does not offer a place to enter a coupon code when buying a game. Instead, the service relies on virtual coupons in your inventory. These coupons are automatically applied when you purchase an applicable game. If you don't use a coupon by its expiration date, it automatically disappears from your inventory.
Using Steam Coupons
Select any of the coupons in your Steam inventory. Most of the time, coupons apply to a single game, but some can apply to any title in a series or by a specific developer. Click "View Applicable Games" under the coupon to reveal which titles can benefit from the discount. When you purchase an applicable game, the coupon is automatically applied at checkout; it will even apply if the game is currently on sale, unless the terms state otherwise.
Getting New Steam Coupons
Users obtain coupons by crafting Steam badges with trading cards (see Resources). You'll also get new coupons during Steam holiday sales and for owning certain games. Some publishers automatically provide coupons for another game they sell if you purchase one of their games. While you can't sell your coupons through the Marketplace, you can trade coupons with any user; this helps you get rid of coupons for games you already own and doubles of coupons.
- link Steam: Steam Coupons